1. Field of the Invention
The present invention relates to a plasma display panel, and more particularly, to an electrode structure of a plasma display panel capable of improving brightness and efficiency.
2. Description of the Background Art
Generally, in a plasma display panel (hereinafter, referred to as ‘PDP’), barrier ribs formed between a front glass and a rear glass made of soda lime glass constitute a single unit cell. When an inert gas having a small amount of xenon (Xe) added thereto is discharged by a high frequency voltage using neon (Ne), helium (He) or a mixed gas (Ne+He) of Ne and He as a main discharge gas, vacuum ultraviolet rays are generated to radiate a phosphor material formed between the barrier ribs, thus implementing an image.
Such a PDP is an image display device using a plasma discharge of an inert gas in a minute space of 0.1 mm to 1 mm in length compared to the cathode ray tube (CRT) that was a main kind of a conventional display means. The PDP has characteristics that its manufacturing is easy due to simple structure and a wide screen is possible due to a thin exterior and low power consumption. Accordingly, the PDP has been spotlighted as a next-generation display device.
In case of a PDP that has been usually used, power versus luminous efficiency is 1 to 1.5 lm/W. On the contrary, in case of a sample PDP for test, power versus luminous efficiency is 2.0˜3.0 lm/W. The reason why the luminous efficiency in the test sample is higher than the luminous efficiency of the PDP that is usually used is not due to structural improvement but that the amount of Xe within a gas injected into the discharge space is added more about 14% than an average amount.
If the amount of Xe added increases, power versus luminous efficiency can also increases. However, there are adverse effects in that abrasion of a front panel electrode increases and a sustain voltage for maintaining a discharge increases. Also, even in driving the panel, a cooling effect of electrons increases due to the increased amount of Xe. Thus, a time delay phenomenon that the start of a discharge is delayed occurs.
FIG. 1 shows an electrode structure of a front substrate in a conventional plasma display panel having a long column structure.
Referring to FIG. 1, the front substrate of the conventional long column structure PDP includes discharge cells demarcated by barrier ribs 300, and a scan electrode 210 and a sustain electrode 220 each of which has a transparent electrode 200 and a metal electrode 100. In FIG. 1, reference numeral 10 indicates a distance between the transparent electrodes 200 and 400 schematically shows that a discharge is generated.
In the PDP of the long column structure, a phosphor material is excited by a gas discharge in a negative glow region, radiating light and a discharge is performed utilizing a positive column region in which an excitation characteristic of Xe is high.
If a PDP has a discharge period in which a distance 10 between the transparent electrodes 200 is 300 μm, there exists a positive column region between the transparent electrodes.
Power versus luminous efficiency in the negative glow region is 1 to 2 lm/W, whereas power versus luminous efficiency in a discharge utilizing the positive column region is 7 lm/W or more. Therefore, in order to expand such positive column region, the distance 10 between the transparent electrodes 200 is made 300 um or more.
FIGS. 2, 3 and 4 are views shown to explain the principle of discharge start and discharge sustain in the plasma display panel having the long column structure.
Referring to FIG. 2, negative charges are accumulated in the scan electrode 210 and positive charges are accumulated in the address electrode 230, by means of a reset waveform applied to the electrode when the PDP is driven. Thereafter, if a negative voltage is applied to the scan electrode 210, the distance 10 between the transparent electrodes 200 of an upper plate becomes greater than a distance 20 between the upper plate and the lower plate. Therefore, a weak discharge 600 occurs between the scan electrode 210 of the upper plate and the address electrode 230 of the lower plate.
By reference to FIG. 3, electrons are diffused toward the sustain electrode 220 by means of a potential difference between the scan electrode 210 and the sustain electrode 220, thereby forming a positive column region 700. A negative glow 710 discharge region formed by an initial discharge is located between the scan electrode 210 of the upper plate and an address electrode 230 of the lower plate. The positive column region 700 is maximized and expanded to the sustain electrode 220.
In case of the plasma display panel of the above long column structure, however, luminous efficiency can be increased, whereas a distance between transparent electrodes in the panel becomes 300 μm or more. Therefore, there are problems in that a voltage for maintaining a discharge of a discharge space increases and a discharge start voltage rises.
Furthermore, in a common PDP, the amount of voltages applied to RGB cells in order to maintain the same color temperature can be different because brightness characteristics of RGB phosphor materials are different. In this case, there is a problem in that overall driving efficiency is lowered since an erroneous discharge occurs in the RGB cells.